var google = require('googleapis');
var discoveryDoc = 'path/to/discovery.json';

google.discoverAPI(discoveryDoc, function (err, jobs) {
  if (err) {
    console.error('Failed to generate jobs client!');
    throw err;
  }

  var key = require('path/to/your/key.json');
  var jwtClient = new google.auth.JWT(key.client_email, null, key.private_key, ["https://www.googleapis.com/auth/jobs"], null);

  jwtClient.authorize(function(err, tokens) {
    if (err) {
      console.log(err);
      return;
    }

    jobs.companies.list({ auth: jwtClient }, function (err, result) {
      if (err) {
        console.error('Failed to retrieve companies!');
        throw err;
      }

      console.log('Companies:', result);
    });
  });
});